The power of individual semiconductors lasers is limited by bulk and surface material damage. Power scaling involves combining many diode lasers. The brightness of an array, however, is not as large as a single laser with the same power unless the emitters can be made coherent with each other.
Coherent coupling of diode arrays has long been approached by letting adjacent gain channels evanescently couple to each other and lock into a large effective spatial mode, sometimes dubbed a supermode. Because the interchannel spaces are lossy, the lasers are encouraged to lock in an antiphase pattern, where the phase of alternate channels reverses in sign, and there are intensity nulls between channels. The emitted field with its modulated spatial phase propagates into the far field as a beam with more than one lobe. This weakens the goal of high brightness.
In one proposed diode laser array, the phase of each output beam is individually controlled with an electrical current such that the output beams are coherent in phase with each other. This method, however, requires electrical circuitry to actively control each diode laser in the array, which increases the cost and size of the array. Moreover, this method may also be difficult to scale to a large number of diodes.
In light of the above, there exists a need for a scalable system and method of coherently coupling output beams in phase with each other.